The proximate cause for the encoding of this character was the need
to provide roundtrip mapping for encoded characters in ISO 5426-2:1996,
Information and documentation -- Extension of the Latin alphabet coded
character set for bibliographic information interchange -- Part 2:
Latin characters used in minor European languages and obsolete
typography.

That standard has four characters annotated as "Used as a binding signature
mark," 0x32 REFERENCE MARK, 0x34 MALTESE CROSS, 0x36 RIGHTWARDS LEAF ARROW,
and 0x37 LATIN CAPITAL LETTER SIDEWAYS Q. The first three were unified with
the existing Unicode characters U+203B REFERENCE MARK, U+2720 MALTESE CROSS,
and U+2767 ROTATED FLORAL HEART BULLET (aka "hedera" or "ivy leaf"). The
sideways Q could not be unified with any existing character, and so was
encoded as a new character.

Binding signature marks are marks placed by publishers on the edges of
signatures (aka "gatherings" -- printed and folded sheets in units of
8, 12, 16, 24, or 32 pages) for book binding. There are a rather large
number of these, which could be considered publisher logos, in a way,
except that many of them make use of odd symbols available in their
printers' type sets. There is no particular need to go out and catalog
more of them and encode them as characters, because of their peculiar
usage not part of regular text. However, the ROTATED CAPITAL Q got in
as part of the mapping project to help get ISO TC46 out of the business
of developing and maintaining character encoding standards independently
of the ongoing work in ISO JTC1/SC2/WG2 to develop ISO/IEC 10646.

--Ken

P.S. One more in the series of contributions to the massive opus known
as "Every Character Has a Story."